In this proposal we will combine mosquito microsurgery with biochemical and light and electron microscopical techniques to investigate the role of the head, ovaries, midgut, and the blood meal in the initiation and maintenance of vitellogenin synthesis by the fat body and the uptake and processing of vitellogenin by the oocytes. We will use extracts of the head to investigate the role of head factors in vitellogenin synthesis and processing, defecation, and non-reproductive metabolism. Initially, we will concentrate on the physiological aspects of these problems in order to develop practical bioassays for the active factors in our extracts. We propose to investigate the ovarian inhibitory factor, produced by ovaries retaining mature oocytes, to determine whether it acts by blocking the release of neurosecretory factors from the head. We also want to determine the role of this inhibitor, as well as neurosecretory factors from the corpus cardiacum, and releasing factor from the ovaries, on the second gonotrophic cycle after a new blood meal. We will continue investigating the endocrine-like cells in the midgut, their distribution, changes in secretory granule content under different dietary conditions, and their immunoreactivity to vertebrate peptide hormones. We will also use immunocytochemistry at both the light and EM level to study the synthesis of trypsin and its release after a blood meal. Control of adult mosquitoes still depends largely on broad-spectrum hydrocarbon insecticides. More selective methods of control will require a more thorough knowledge of vector behavior, and an understanding of vector behavior must be based on an understanding of their physiology. New information about mosquito reproductive endocrinology will not only increase our knowledge of vector behavior but will also have the potential for application in novel methods of control, e.g., "third generation pesticides."